The present invention relates to a force sensing disc drive slider, and more particularly to a disc drive slider having a capacitance sensor responsive to forces acting on a contact pad that does not affect the aerodynamic characteristics of the slider.
In a disc drive system, the contact force between a slider carrying a transducing head and a disc media perpendicular to the surface of the disc media is a very important parameter. It is desirable to accurately measure this force in order to obtain a quantitative understanding of a variety of head-to-disc interface phenomena such as friction, vibration and wear, for example, particularly in planar slider systems where the transducing head is somewhat exposed at the air-bearing surface. These measurements enable slider glidability, seek and take-off characteristics to be analyzed for potential improvements in the slider architecture. The debris generation and wear characteristics of the head-to-disc interface could also be measured through mapping of the contact force measurements. The uniformity of the surface of the disc media could be tested and certified by analyzing these measurements. Other applications utilizing quantitative measurements of the contact force between the slider and disc media perpendicular to the disc surface will be apparent to one skilled in the art.
In order for the contact force measurements to be useful, the slider incorporating the contact force sensor must exhibit the same aerodynamic behavior as an actual slider for carrying a transducing head. Therefore, the contact force sensor must be implemented within the physical dimensions of an actual slider. The fabrication of the contact force sensor should not affect the fabrication process used in forming the air-bearing surface (ABS) of the slider. The resulting slider containing the contact force sensor must be attachable to a suspension in the same manner as a head-carrying slider, and the wire leads of the force-sensing slider should be located in a manner similar to the head-carrying slider.
Attempts have been made to estimate the contact force between the slider and disc media indirectly using acoustic emission signals. However, the physical phenomena occurring in this acoustic emission process are extremely complicated, such that some sort of direct measurement is necessary as a reference or calibration point for this method to yield results with any level of accuracy.
Another approach to measuring the contact force at the head-to-disc interface has been to incorporate a piezoelectric element onto a test slider, with the voltage across the piezoelectric element representing a strain force applied to the piezoelectric element due to forces acting on the test slider. While this approach is able to detect forces acting on the slider, such as forces due to the slider contacting debris or an asperity on the disc surface, it is difficult to isolate the z-component of the force (perpendicular or normal to the nominal disc surface) from the overall signal. The signal interpretation process to determine this perpendicular force component is extremely complex, and involves significant material research.
Therefore, there is a need in the art for a readily implemented contact force sensor for use with a standard slider, with minimal signal interpretation involved in analyzing the contact force at the head-to-disc interface perpendicular to the surface of the disc media.